This application relates to the art of thermostats and, more particularly, to thermostats having internal heaters for supplying auxiliary heat to a bimetal disc and thereby making the thermostat responsive to lower external temperatures. The invention is particularly applicable to thermostats that have a bimetal disc for operating a single pole single throw switch and will be described with specific reference thereto. However, it will be appreciated that the invention has broader aspects and can be used in other types of thermostats.
U.S. Pat. No. 4,533,894 issued Aug. 6, 1985, discloses a thermostat having internal heaters for providing temperature depression. The arrangement described in the patent provides temperature depression up to a maximum of about 15.degree. F. because the thermal rating of the plastic thermostat housing limits the amount of heat output from the internal heaters that can be tolerated. Electrical spacing requirements also prevent location of the heaters too close to the bimetal disc. It would be desirable to have a thermostat of the type described that was capable of significantly greater temperature depression than about 15.degree. F. and that could have the internal heaters positioned extremely close to the bimetal disc.